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Research shows managed fire benefits forest carbon sequestration

November 28, 2012

Research shows managed fire benefits forest carbon sequestration

UNIVERSITY PARK, Pa. -- With the current focus on carbon emissions affecting climate change and the critical role forests play in storing the element, a better understanding of the impact that fire has on the global carbon cycle is needed by policymakers, according to a researcher in Penn State's College of Agricultural Sciences.

As carbon registries, carbon credits and carbon trading become more important in the coming years, managed fire should play a major role in managing forests for both ecological and carbon-sequestration reasons, contends Matthew Hurteau, assistant professor of forest resources.

Hurteau -- who for six years has been studying carbon markets, the carbon cycle and forests' ability to lock up varying amounts of the element under changing conditions -- is seeking to alter perspectives about the effect of fire on carbon sequestration. His research has involved both field studies and modeling to address a range of topics, including forest carbon, wildfire, species diversity and productivity.

"We are losing the fire-suppression battle because we have such a huge accumulation of fuel on many forest floors in the West," he said. "Fuel accumulation, combined with more extended droughts and higher temperatures, result in much longer, more severe fire seasons. We are seeing a substantial increase in the amount of land area burned over time."

That matters because forest fires release carbon into the atmosphere. However Hurteau's research indicates that more fires -- but managed and less severe -- combined with thinning stands of trees, actually benefit carbon markets because the amount of carbon locked up by forests that are managed with prescribed fire is greater.

"It is a question of having less frequent but really large fires or more frequent but smaller, prescribed burns," he explained. "The difference between those two is the severity of the fire. These huge, severe wildfires we have been seeing kill most of the trees involved because the flames don't only touch the surface of the forest, but they also burn up into the canopy.

"But with a more frequent fire regime, we have surface fire that is not burning nearly as hot and is not getting up into the canopy, resulting in much lower tree mortality. So overall, more frequent but less-severe fires give off less carbon, but more importantly more of the carbon is locked up in surviving trees that will continue to grow and sequester more carbon."

Hurteau hopes his recent research journal article, "Aligning Ecology and Markets in the Forest Carbon Cycle," published this fall in Frontiers in Ecology and the Environment, will further the discussion that prescribed fire is beneficial for both ecological and carbon-sequestration purposes.

"If we manage forests based on their specific ecology, we lower the risk of carbon loss due to wildfire," he said. "By allowing small fires and reducing tree density, we make the carbon-offset system more resistant to the effects of natural disturbances."

-- Convince forest managers that managed, less-severe fires that do not burn up into the canopy and kill trees can be a benefit to carbon sequestration, even though they result in emissions. He calls this "reconciling the science-policy divide."

-- Persuade the scientific community that while looking at the carbon cycle from a global perspective relative to climate change is valuable, forest-management decisions are made locally, making the smaller market scale important for climate change mitigation. "Think globally, value locally," he said.

The idea behind cap-and-trade programs for mitigating climate change is that greenhouse gases stored in one place can offset emissions from somewhere else, thereby reducing total emissions, Hurteau explained. Forest growth removes carbon dioxide from the atmosphere and represents one type of emission offset.

Forests provide an ecosystem service by pulling carbon dioxide out of the atmosphere and, through photosynthesis, turning it into wood, locking up the carbon. When fire reverses that process by burning the woody fuels and killing trees, carbon gets emitted back into the atmosphere.

"The ability of forests to sequester carbon dioxide from the atmosphere has captured the attention of policymakers, nongovernmental organizations and a burgeoning number of offset project developers," he said. "The underlying concept is simple: sequester carbon from the atmosphere by reforesting degraded lands, thereby increasing the amount of carbon stored in current forests or reducing forest loss.

"However, implementing a system to quantify and monetize -- place a dollar value on -- this mitigation benefit requires attention to details that will help ensure that the forest offset is actually equivalent to the emission it is meant to compensate for. Disturbances such as severe fires disrupt the system."

Registries seek to ensure that their carbon offsets are equivalent to reductions in fossil-fuel emissions. Once a unit of forest carbon is quantified, registered and sold, it is tied to carbon stored in trees or wood products within a specific project boundary. If the unit of carbon is lost through a disturbance event, it is counted as an emission and must be reimbursed.

If a unit of forest carbon is monetized and sold, and then a disturbance releases that sequestered carbon, it must be replaced with an equivalent unit of carbon to ensure that the climate-change-mitigation goal of the carbon registry is met -- maintaining system integrity.

"Thus, wildfire-mitigation actions that have been shown to improve the stability of forest carbon stocks, such as forest thinning and prescribed burning, are beneficial," Hurteau said. "Yet, the global carbon cycle perspective that is common in the forest science literature often fails to consider the consequences of wildfire occurring in a specific offset project."

Hurteau said he believes that classifying tree-stand thinning and prescribed burning as forest degradation is misguided and needs to change.

"When we get fixated on mitigating climate change and we look at a forest as just a place to store carbon -- if that becomes our primary objective -- it's a mistake," he said. "What we really should be doing is managing these systems based on their ecology and looking at carbon sequestration as an ancillary service that the ecosystem provides."

Hurteau's research collaborators include Bruce Hungate and George Koch, Northern Arizona University in Flagstaff, Ariz.; Malcolm North, U.S. Department of Agriculture Forest Service Pacific Southwest Research Station and adjunct faculty member at University of California, Davis; and Gordon Smith, Ecofor LLC, a forest-consulting firm in Seattle.